Aneurysms of the aorta can involve either the aorta in the thoracic cavity (thoracic aortic aneurysms or TAA) or in the infrarenal aorta in the abdominal cavity (abdominal aortic aneurysms). We have identified families with autosomal dominant inheritance of TAAs and/or aortic dissections. Family members have been evaluated in the UCRC and blood drawn for DNA harvest. We have characterized 10 families with autosomal dominant inheritance of TAAs and or aortic dissections, in which there is decreased penetrance and variable expression. We have used the DNA from the families to determine the chromosomal location of the defective gene causing this condition using polymorphic markers spaced throughout the human genome and linkage analysis. The defective gene has been mapped to a 4 cM region on one of the autosomal chromosomes and there is not evidence of genetic heterogeneity. Therefore, we hope to identify a gene involved in the etiology of thoracic aortic aneurysms and dissections, which will be useful in the future to identify individuals at risk for aneurysms and dissections, and prevent premature deaths. These should also provide information on the proteins that give structural integrity to the thoracic aorta.